Trailer brake control system

ABSTRACT

Systems and methods are provided for controlling operation of a trailer brake system associated with an agricultural vehicle, comprising: determining a coupling force associated with a coupling point for providing a coupling between the vehicle and a trailer, determining, in dependence on the coupling force, the presence of a trailer coupled to the vehicle at the coupling point; and controlling one or more components of the vehicle in dependence on the determination of the presence of the trailer.

FIELD OF THE INVENTION

The invention relates to a control system for a vehicle trailer brake,especially for use in agricultural vehicles such as tractors.

BACKGROUND

Many vehicles are provided with attached trailers for the transportationof goods and materials. For large-scale use such trailers may beprovided with trailer braking systems to allow for safe control of thetrailer, and to prevent jack-knifing or skidding of the trailer whenbraking.

Both jack-knifing or skidding occurs when the force applied by thetrailer to the towing vehicle, also referred to as coupling force,exceeds a certain level. The coupling force is mainly generated by thetrailer weight and the inertia during breaking. A first effect of anexcessive coupling force is that the towing vehicle is excessivelypushed (later referred to as push condition) and the vehicles trackguiding forces are overcome. This results in a yaw moment/movement aboutthe vertical vehicle axis of the towing vehicle which cannot be bear bythe wheel-ground contact. The towing vehicle then starts to skid.

A further effect may be that in case of drawbar trailer wherein thefront wheels are pivotably attached to the trailer chassis the drawbarmay be unintentionally be pivoted relative to the chassis by thecoupling force so that the trailer behaves like the jack knife andswerve out of its track.

These effect is especially appearing when the vehicle is deceleratedwithout the driver activating the vehicle service brake system andoccurs when downshifting a continuously variable transmission or using aretarders in trucks.

It is well known that these effects can be reduced by activating thebrakes of the trailer depending on the coupling force to stabilize thevehicle combination. But the brake activation must be appropriatelyapplied to reduce the coupling force but also to avoid that excessivebraking destabilizes the vehicle combination as the combination isstretched excessively which would also apply a yaw moment to towingvehicle.

With the introduction of electronic braking systems wherein the brakeforce can be controlled independent of the drivers input systems havebeen developed especially for trucks.

Therefore, trailers used in combination with trucks are mainly usinginformation of on-board assistant systems like electronic trailersuspension, ABS, ESP, ASR to determine the coupling force. Especiallythe trailer suspension helps to determine the weight of the trailer,other of these sensors help to fine tune the brake actuation bydetermining wheel speeds and accelerations.

Focusing now on agricultural vehicle combinations, mainly tractors andagricultural trailers, it must be considered that brake systemsdescribed above are not as common as for trucks. Especially the trailersare rarely equipped with on-board assistant systems like electronictrailer suspension, ABS, ESP, ASR and therefore the coupling force isdifficult to determine.

It may be advantageous to monitor the health of trailer brake systemswherein the brake force is controlled independent of the drivers inputsystems. One such example of a potential fault is known as “brakefading”, resulting from brake element overheating. EP1 441 938B1suggests to install brake temperature sensors close to the brake disc todetermine the temperature of at least on brake assembly. As mentionedabove. trailers towed by agricultural tractors are simple in design andnot equipped with such sensors.

It is therefore a further target of the invention to determine thetemperature of the trailer brakes based on parameters which are alreadyinstalled on the tractor to keep costs down and reduce complexity.

A known method to determine trailer brake temperature uses trailer brakesignal (or pressure) and the duration of the brake actuation generatedby the tractor control system. Such a method is described in EP1 441938B1. However, in such systems temperature warnings may generated evenwith no trailer in use. It is therefore advantageous to be able todetermine if a trailer is connected to the tractor, and furthermore, ifthe towed trailer is equipped with a trailer brake system. It is commonin agricultural operation to use trailers (or more commonly implements)which are fully attached to the three-point linkage but do not havewheels which are braked. So detecting the trailer or an implement justbased on the recognition of the trailer current supply connector (whichis a standard connection to supply lights etc. on the implement) is notsuitable as the implement may not have a trailer brake system even ifthe connection to trailer current supply connector is detected.

So it is a further target of the invention to generateinformation/warnings to the driver considering the state of animplement/trailer attached.

Further, if the known method to determine trailer brake temperaturebased on trailer brake signal (or pressure) and the duration of thebrake actuation (generated by the tractor control system) is used thetemperature determination may be inappropriate as influencing parameterssuch as the weight of the trailer are mostly not known for agriculturaltrailers.

So it is a further target of the invention to improve the known methodfor trailer brake temperature determination using further availableparameters of the tractor to determine the trailer brake temperaturemore accurately.

It is an objective of the invention to provide a trailer brake controlsystem which overcomes the aforementioned problems to determine thebraking force applied to a trailer.

SUMMARY OF THE INVENTION

According to an aspect of the invention there is provided a controlsystem for controlling operation of a trailer brake system associatedwith an agricultural vehicle, the control system comprising a vehiclecontrol unit, and being configured to: determine a coupling forceassociated with a coupling point for providing a coupling between thevehicle and a trailer; determine, in dependence on the coupling force,the presence of a trailer coupled to the vehicle at the coupling point;and generate and output a control signal for controlling one or morecomponents of the vehicle in dependence on the determination of thepresence of the trailer.

A further aspect of the invention provides a braking system comprisingand/or being controllable by a control system of the preceding aspect ofthe invention.

A further aspect of the invention provides an agricultural vehiclecoupleable to a trailer to form a vehicle-trailer combination, andcomprising and/or being controllable by a control system as describedherein.

A further aspect of the invention provides a method of controllingoperation of a trailer brake system associated with an agriculturalvehicle, comprising: determining a coupling force associated with acoupling point for providing a coupling between the vehicle and atrailer; determining, in dependence on the coupling force, the presenceof a trailer coupled to the vehicle at the coupling point; andcontrolling one or more components of the vehicle in dependence on thedetermination of the presence of the trailer.

Further advantageous embodiments and features are described herein withreference to the following description and/or the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, withreference to the accompanying drawings in which:

FIG. 1 schematically represents side view of a vehicle combination usingthe present invention,

FIGS. 2, 3, 4, 5 are flow charts showing the principal process steps ofa method embodying the invention.

FIG. 6 a schematically represents side view of a vehicle combination andthe forces applied using the present invention,

FIG. 6 b is a characteristic map showing the resistance force dependingvehicle speed, and

FIG. 7 is a characteristic map showing the results of method to controlthe trailer brake control signal (TBS) according to the invention.

FIG. 8, 9, 10 are flow charts showing process steps of methods accordingfurther embodiments of the invention,

FIG. 11A/11B are flow charts depicting the process steps as shown inFIGS. 5 but added with process steps of methods according furtherembodiments of the invention,

FIG. 13A, 13B, 13 c, 13 d show simplified representations of thegraphical warning messages according further embodiments of theinvention, and

FIG. 14A, 14B are characteristic maps showing the results of methodaccording further embodiments of the invention.

It will be understood that the term “trailer” as used herein is similarto the terms “attachment” or implement” which is more commonly used inthe context with agricultural vehicles such as tractors.

DETAILED DESCRIPTION

FIG. 1 shows a vehicle combination 1 comprising a tractor 10 and atrailer 20 which is attached to the tractor hitch system 11 of thetractor 10 via a trailer drawbar 21. The tractor 10 comprises front andrear wheels 5, 6 which are braked by a service brake system and a parkbrake systems which is not described hereinafter in detail as well knownin the art. To brake the trailer, a trailer brake system 30 mainlyincluding a trailer brake valve 30 a and or further valve arrangementsand is provided to forward a pneumatic or hydraulic brake signal to thetrailer via the standardized trailer control coupling 31. The furthertrailer supply coupling 32 is provided for air or oil supply to thetrailer brakes. Both couplings 31, 32 are used to connected at least thetrailer brake system 30 to a brake system 40 of the trailer. The brakesystem 40 serves to actuate the brakes of the wheels 25 of the trailer20.

The trailer brake actuation pressure can be generated by trailer brakesystem 30 e.g. when the driver activates the service brake system withthe brake pedal (not shown) and/ or the park brake system (with thehandbrake lever) of the tractor 10 so that brake demand is directlyforwarded by pressurized fluids such as air or oil to the trailer brakesystem 30. Alternatively a trailer brake actuation pressure may begenerated independent of the direct driver activation but in response toa trailer brake signal TBS coming from an electronic vehicle controlunit ECU, which is also referred to as electronic trailer braking. Thistype of brake signal generation is focused in the following invention.

To provide a control system for the trailer brake of the trailer 20, thetractor 10 the electronic vehicle control unit ECU receives parameterand/or sends control signals to various components of the tractor 10,including the following. A transmission 50 to adjust the vehicle speed vor the vehicle acceleration a depending on the demand set values of thedriver and receive parameters such as the output rotational speed androtation direction of the output shaft of the transmission and thesystem pressure of the hydraulic branch of the CVT (continuous variable)transmission 100. A gyroscope 60 to determine vehicle speed v or thevehicle acceleration and/or inclination α. The gyroscope may be part ofa satellite based navigation system. A speed foot paddle 71 and/or adrive lever 72 to receive the drivers input for vehicle speed or avehicle acceleration. An acceleration rate input 73 to adjust the degreeof acceleration/deceleration when moving the drive lever 72. A clutchpedal 74 to disconnect the transmission 50 from the prime mover such asan internal combustion engine. A HMI terminal 75 to enable the driver toinput or display various parameters in connection with the vehicle 10,the trailer 10 or the vehicle combination 1. A service brake foot paddle76 to receive the drivers input for the activation of the service brakeof the tractor. A park brake switch or a park brake lever 77 to receivethe drivers input for the service brake for the activation of theservice brake of the tractor.

To summarise, the electronic vehicle control unit ECU has the major taskto provide a processing method which includes: receiving relevantparameters of the vehicle 10; determining a set value for the trailerbrake signal TBS according the method described hereinafter; andforwarding the trailer brake signal TBS to the trailer brake controlsystem 30 to activate the trailer brakes.

In the shown embodiment, the trailer brake signal TBS is represented bya pressure demand to control a pneumatic trailer brake system 30.Alternatively, the trailer brake signal TBS may be provided to control ahydraulic brake system and the trailer brake valve 30 a is alsohydraulically operated. More alternatively, the trailer brake signal TBSmay be forwarded to the trailer brake system by any other means such asan electronic signal if brake-by-wire systems are installed on thetrailer.

The method for controlling the trailer brake control system 30 will nowbe described with reference to the flowchart of FIGS. 2, 3, 4, 5 .

The method can be implemented on the electronic vehicle control unit ECUor may alternatively be part of the trailer brake control system 30 whenequipped with a respective control unit and interface to receive theabove mentioned parameters.

According the ongoing method, the electronic vehicle control unit ECUiteratively generates a trailer brake signal TBS to be forwarded to thetrailer valve 30 a. The trailer brake signal TBS receives differentvalues which are described hereinafter.

The electronic vehicle control unit ECU executes the method M100 asdepicted in FIG. 1 . For clarity reasons, the main method M100 isdepicted in several sub processes wherein FIG. 2 shows the main methodM100 which includes sub process S200 as shown in FIG. 3 , sub processS300 as shown in FIG. 4 and sub process S400 as shown in FIG. 5 .Further sub processes S500, S600, S700 are described below.

Referring now to FIG. 2 , the electronic vehicle control unit ECU isinitializing the method with step S100. The initialization may betriggered if the ignition is ON and the electronic vehicle control unitECU is energized. Alternatively, the initialization may be triggered ifthe electronic vehicle control unit ECU detect that a trailer 20 isattached to the vehicle 10. This may be determined if the standardizedcurrent supply connector (which supplies current to the trailer 20and/or activates lights or the turn indicator of the trailer 20) isconnected to the receiving connector on vehicle 10.

After initialization, the methods checks with step S105 if theelectronic trailer brake function is activated (with ETCV=1) and thenbranches off to subroutines in step S200, S300. The electronic trailerbrake may be activated when ignition is ON and the electronic vehiclecontrol unit ECU is energized or may be activated/deactivated by thedriver input initially. Alternatively electronic trailer brake maytemporarily be aborted by actuation of the service or park brake.Deactivation of the trailer brake function results in the parameterETCV=0.

In subroutine S200 several pre-conditions and activation parameters forfurther proceeding in method M100 are checked which are depicted in FIG.3 . The term pre-condition means that these conditions must be met togenerally enable activation of the electronic trailer braking whileactivation parameters serve to determine what event causes decelerationand additionally may establish the degree of deceleration and to adaptthe trailer brake signal accordingly.

After starting at S201, step S205 (re)sets status parameters SP_(DL),SP_(AS), SP_(CA), SP_(CC), SP_(REV), SP_(ENG), to zero. The statusparameter are explained lateron.

Generally the activation checks pre-conditions which allow theelectronic trailer brake function is to be activated and whether and howthe vehicle is decelerated, especially but not exclusively if this isdone by using the acceleration foot paddle 71 or the drive lever 72.Furthermore, this step serves to determine the driver's demand regardingthe degree of deceleration, also referred to as the driver decelerationdemand DD.

These pre-conditions try to avoid unsafe vehicle caused by electronictrailer braking but also serve to avoid unmeant or unnecessaryelectronic trailer braking resulting in that the driver may feeluncomfortable when the assistance system activates trailer brake when itis apparently unnecessary. In other words, electronic trailer brakingshall be prohibited when not needed.

Step S206 a checks a first pre-condition by determining if the couplingforce F_(C,real) (see subroutine S300) is below a set value ofF_(CA,min), say −3500 N (in a range of negative sign) to ensure that thetrailer 20 significantly pushes the tractor 10 (push condition). Thereare conditions, in which higher coupling force F_(C,real) (smaller whenseen with negative sign) may occur but electronic trailer brake shouldnot be activated. E.g. this condition may occur if an implement isinitially coupled to the tractor or if potholes are passed. If NO, theprocess returns prior to step S206 a with loop L207.

Step S206 a must be seen as a pre-condition which, when once met,enables the coupling force F_(C,real) to take any value in the furtherprocessing, even being above F_(CA,min) without aborting the process orthe activation.

In the next steps, a series of further pre-conditions are checked:

Step S210 a checks if the driveline clutch is activated. This provisionis necessary when e.g. the operator intends to let the vehiclecombination roll towards a crossing. The method should not be executedfurther as this results in that the CVT is drivingly disconnected fromthe wheels so that the determination of the coupling force based on CVTparameters is not possible. So if YES step S210 b is proceeded to checknext pre-condition while NO would be followed by step S220 explainedlateron.

The step S210 a is provided subsequent to step S206 a (which requiresthe detection of a coupling force when clutch is disengaged) to makesure that the activation is aborted whenever clutch is subsequentlydisengaged.

Next, steps S210 b and S210 c proceed to check two pre-conditions in anOR relationship which means that one of both is met. According step S210b the vehicle speed shall be v_(v)>0 kph (or alternatively V_(SET)>0kph) or according step S210 c the tractor 10 drives uphill withα<α_(CA,max), of say −4° as a negative sign is downhill inclination, asboth conditions are known for resulting in push condition.Alternatively, step S210 b may consider a minimum value for the vehiclespeed v_(v) or vehicle speed set point VSET to be exceeded to avoidelectronic trailer activation at low speeds where push condition is lesscritical. When one of these pre-condition is met, the method proceeds tostep S220 explained lateron. Otherwise, next pre-condition is checked instep S210 d.

Step S210 d is provided to avoid that electronic trailer braking isactivated in stand still on plane ground (no or small slope). Thereforestep S210 d checks if v_(v)=0 kph (or alternatively v_(SET)>0 kph) andthe slope is close to zero. This is especially important when a CVT isinstalled having so called “active standstill” control: If the vehicleis decelerated by speed foot paddle 71 or a drive lever 72 to standstill(0 kph) without service or park brake being activated, the CVT isoperated in “active standstill”. In this condition, the electronicvehicle control unit ECU provides control of the transmission tomaintain the output speed of the transmission (and thereby the wheels)at zero rpm to compensate unmeant movement resulting from idle oil flowin the hydraulic branch of the CVT (as described in applicant'spublished patent applications EP 1 990 230 and EP 2 935 948). Thismeans, that the hydraulic units are permanently adjust which may resultin that a coupling force may be detected which should not result intrailer brake activation.

So to summarize, the steps S210 b, S210 c and S210 d serve to enableelectronic trailer braking when driving on even ground, uphill ordownhill and when the tractor stands still on downhill as push conditionmay be present. But when standing uphill or on even ground, activationshall be prohibited as these conditions will not result in pushcondition.

When step S210 d results in YES, the loop L210 returns prior to step 210with status parameters SP_(CA) remaining zero.

Alternatively further pre-conditions may be checked indicated by stepS210 d and may result in further processing of step S220 or a loop whichreturns prior to step 210 with status parameters SPCA remaining zero.

Further pre-conditions not shown in FIG. 3 may be:

-   -   CVT switch to “neutral”: In this operating condition activated        via HMI terminal, the CVT is brought into a condition similar to        the clutch engaged described in step S210 a with the CVT        drivingly disconnected from the wheels so that the determination        of the coupling force based on CVT parameters is not possible.    -   Condition “EU brake test”: This condition is activated by the        driver to inhibit actuation of the service brake function of the        trailer brakes when the park brakes on the tractor are applied        in standstill. This test procedure must be regularly done due to        EU regulations to check if the park brake system of the tractor        (energised by spring load) is capable to sufficiently keep the        vehicle combination in standstill (when shut down) if the        trailer brakes may fail due to leakage/malfunction in the        trailer brake system. The electronic trailer brake must be        permanently deactivated during the test without unmeant trailer        brake actuation.    -   Electronic trailer brake function activated: Similar to step        S105 (in FIG. 3 ) the electronic trailer brake function must be        activated (with ETCV=1).    -   Maximum speed requirement: If the vehicle speed exceeds 25 kph.        Above a certain vehicle speed, the wheels tend more to lock when        braked. Especially at high speeds, this may cause dangerous        situations so the method is prohibited above a certain vehicle        speed The maximum vehicle speed value may be determined        depending on the driver's choice or may also set dependent on        trailer parameters. E.g. If the trailer is equipped with ABS        system, the limitation may not be necessary.        With the following steps, the method detects in which way the        operator inputs a demand to decelerate the vehicle (without        actuating service or park brake). This is done in activation        branches B211, B212, B213, B214 and B215. Activation branch B211        commences with step S220, in which the activation via the drive        lever 72 is checked. If the operator intends to decelerate the        vehicle, he pushes back the drive lever 72 in the opposite        direction as indicated with arrow DR. Thereby, the demand value        V_(DL) which is forwarded to the ECU is in a minus range and the        parameter V_(DLminus) is set to 1. If the drive lever 72 is        released, vehicle speed remains constant so that parameter        V_(DLminus) is set to 0.

If parameter V_(DLminus) is set to 1, this leads to step S225 in whichthe status parameter SP_(DL) is set to 1 indicating that thedeceleration is inputed via drive lever 72. Next step is step S226 inwhich the value of the acceleration rate input 73 is determined. Theacceleration rate input 73 serves to determine the operators inputregarding the driver deceleration demand DD on response of theoperator's input and therefore offers four set points: level I, II, III,IV. If the operator adjusts the acceleration rate input 73 to level I inwhich the status parameter SP_(AS) would receive the value 1, thedriving speed of the vehicle decreases at slowest so that thedeceleration is low and smooth. At Level IV in which the statusparameter SP_(AS) would receive the value 4 the driving speed of thevehicle speed decreases rapidly and would result in an “aggressive”deceleration.

Alternatively, the drive lever may provide a proportional speed controlwhich means that the acceleration rate depends on the deflection angleor the deflection speed. In this case, an acceleration grade input 73may not be present but the status parameter SP_(AS) would be setdepending on deflection angle or speed.

If parameter V_(DLminus) is set to 0, which indicates that the vehicleis not decelerated via the drive lever 72, activation branch B212 isfurther executed in which further operator inputs are checked.

Therefore branch B212 branches of in branch B213, B214 and B215.

With branch B213 the process checks deactivation of the cruise controlin step S230. If YES, the deceleration via the speed foot paddle 71 ischecked with step S232. The speed foot paddle 71 is depressed by theoperator's foot and forwards the speed demand to the ECU. This isdifferent to the driver lever 72 in that the deflection angle isproportional to the demand value for the vehicle speed. In other words,if fully depressed, the demand is maximum vehicle speed or alternativelyany vehicle speed limit value which the driver can set via the HMIterminal 75. E.g. if the vehicle is operated for shunting, the drivermay set a lower speed assigned to full pedal depression to increase thepedal resolution and enable finer control. If speed foot paddle 71 isfully released (after any depression), the demand for the vehicle speedis zero kph, which means that the vehicle is decelerated. So step S232checks if the pedal mode is activated. If not, depressing the speed footpaddle 71 would not impact the vehicle movement but only adjust enginespeed. As a consequence, the loop L233 returns prior to step S205.

Step S234 checks if the speed foot paddle 71 is completely released(after depression), so that V_(FP) is set to 0. If not, the loop L235returns prior to step S205.

If YES, step S236 sets the status parameter Sp_(DL to) zero. Withreference to step S225, in which the parameter is set depending onoperation of the drive lever 72, status parameter sp_(DL) is generallyproviding the information if speed foot paddle 71 or drive lever 72indicate deceleration.

If step S230 indicates activation of the cruise control, branches B213is proceeded to determine subsequent condition present in cruise controlmode.

Therefore, step S240 determines if the current vehicle speeds exceedsthe set point of the cruise control.

This occurs in a first cruise control condition wherein the set point ofthe cruise control is changed by:

-   -   Firstly, the HMI terminal enable driver to save to set points C1        and C2 for different cruise control set points. Both values can        be pre-selected by pushing a button assigned to C1 and C2 which        may be positioned close or on the drive lever 72. Driver use        this HMI function to e.g. switch from a set point used in the        field or on the road, e.g. if the C1 is 18 kph for field work        and 60 kph for fast travel on roads. The driver activate the set        point of the cruise control by using the drive lever 72. While        the drive lever 72 is used to accelerate or decelerate the        vehicle by moving in driving direction forwards and backwards,        moving the drive lever 72 briefly to the right is used to        activate cruise control. If none of the values C1 or C2 is        pre-selected, the current speed is taken as new set point value.    -   Secondly, the driver can adjust the set point of the cruise        control in the HMI terminal 75 which may also result in a        significant deceleration if the new set point is chosen below        current vehicle speed.

Even if there is no significant set point speed reduction, cruisecontrol mode may still result in a situation where electronic trailerbraking is demanded, referred to as the second cruise control mode. Thismay happen if the vehicle combination drives in cruise control mode onan even course and then enters a downhill passage. The weight of thetrailer would then start to push the tractor resulting in an increase ofthe vehicle speed and a deviation from the set point.

So to summarize, step S240 determines conditions in cruise control modein which the vehicle speed is considerably changed withv_(v)>f_(CAv)*v_(SET) which is when the current vehicle speed v_(v)exceeds the speed set point v_(SET) of the cruise control about a factorf_(CAv). The factor f_(CAv) represents a percentage variation, so thatf_(CAv=)1.05 means that the current vehicle speed v_(v) exceeds thespeed set point V_(SET) about 5%.

If the condition v_(v)>f_(CAv)*V_(SET) is not met, loop L241 returnsprior to step S205.

If the condition v_(v)>f_(CAv)*V_(SET) is met, step S242 sets the statusparameter for activation in cruise control mode SP_(CC) to 1 indicatingthe activation of electronic trailer braking based on a condition incruise control mode.

As in the first cruise control mode the degree of deceleration dependson the setting of the acceleration rate input 73, the status parameterSP_(AS) is stored in step S243 similar to step S226.

As in the second cruise control condition the degree of decelerationdoes not depend on the setting of the acceleration rate input 73, statusparameter SP_(AS) may always set to one single value, say 2, when theset point is not changed but the vehicle speed increases relative to setpoint on downhill drive in second cruise control mode.

A further condition is checked with branch B214 in which the processdetermines reversing of the tractor. Reversing of the tractor or thevehicle combination means that the operation of the tractor is changedfrom a first, say forward direction at a predetermined vehicle speed tothe opposite direction with the same or a preselected vehicle speed. Soreversing always results in deceleration which may cause push conditionso that electronic trailer brake must be activated. Reversing can beactivated by an operator user interface. The tractor is thandecelerated, passes standstill and is changed to the opposite directiondriving without further manual intervention. This function offers acomfortable manoeuvring. e.g. during front loader operation. Reversingof the tractor 10 can be initiated by various inputs:

-   -   While the drive lever 72 is used to accelerate or decelerate the        vehicle by moving in driving direction forwards and backwards,        moving the drive lever 72 to the left is used to activate        reversing.    -   Furthermore, a button is provided nearby the steering wheel,        e.g. on the indicator lever to reverse the tractor 10.

In addition the driver can chose if reversing is provided only bychanging the direction, but with the same speed, or changing directionand decelerate/accelerate to a set point which can be pre-selected inthe HMI terminal 75 for each driving direction. This is advantageousdrivers may prefer to drive slower in rearward driving

So along branch B214 followed by step S250, the method checks if thetractor is reversed. If NO the loop L251 returns prior to step 205.

If the condition is met the status parameter SP_(REV) is set to 1 instep S252 and as the degree of deceleration depends on the setting ofthe acceleration rate input 73, the status parameter SP_(AS) is storedin step S253.

Further branch B215 and step S260 monitors a decrease of the enginespeed. The HMI terminal enable driver to save to set points MAX and MINfor different engine speed set points. Both values can be selected bypushing a button assigned to MAX and MIN which may be positioned closeor on the drive lever 72. Alternatively, tractor 10 may be equipped witha hand throttle (not shown) which enables the driver to directly adjustengine speed via a rotary control. As significantly reducing the enginespeed results in deceleration, step S260 monitors engine speeddifference with Δn_(ENG)>Δn_(CAmax) and if the engine speed is reducedabout more than say Δn_(CAmax)=200 rpm, the status parameter SP_(ENG) isset to 1 indicating the activation of electronic trailer braking basedon engine speed reduction. This branch may additionally include thedetermination of a further status parameter to consider a degree ofdeceleration depending of the absolute value of the difference in enginespeed Δn_(ENG). The bigger Δn_(ENG) is the higher deceleration may be sothere may be different deceleration status parameter values for e.g.Δn_(ENG)=200 rpm or Δn_(ENG)=400 rpm or Δn_(ENG)=600 rpm.

All activation branches B211, B212, B213, B214, B215 merge to step S270in which, when one of the activation requirements in branches B211 toB215 is met, the status parameter SP_(AS) is set to 1, indicating thatthe activation is generally enabled, independent of whether by drivelever 72 or speed foot paddle 71 or any other condition caused theactivation.

With step S250, the method proceeds to step 120 as depicted in FIG. 2 .

Parallel to step S200, the step S300 determines the actual couplingforce Fc, actual by considering various driving dynamic parameters asdepicted in FIG. 4 .

The determination of the actual coupling force Fc, actual is furtherexplained with reference to FIG. 6 a which dramatically depicts theforces exerting on a vehicle combination 1, especially on tractor 10,for the driving condition in which the vehicle combination 1 is drivinguphill and in which the danger of jack-knifing is especially high.

The equilibrium of forces applied on the tractor 10 is well known in theart and results in the following equation:

F _(TRC) =F _(IN)+F_(H)+F_(AR)+F_(R,RA)+F_(R,FA)+F_(C)  (E1)

Wherein

-   -   F_(TRC) is the Tractive Force which must be supplied to wheels        5,6 of the tractor 1 by the IC engine and the transmission 50 to        move the complete vehicle combination 1.    -   F_(IN) is the Inertia Force which applies due to the inertia        when the vehicle is accelerated or decelerated:

F_(A) =m _(v) ·a  (E2)

-   -   F_(H) is the Downhill-slope Force which applies due to the        inertia when the vehicle is driving uphill or downhill:

F_(H) =m _(v) ·g·sin (α)  (E3)

-   -   F_(AR) is the Air resistance Force applied by air resistance and        depends on various factors such as the geometry of the tractor    -   F_(R,RA), F_(R,FA) Is the Roll Resistance Force applied by        rolling resistance between wheel and ground an depends various        parameters such as wheel load and ground/wheel contact        parameters    -   F_(C) Is the Coupling Force which represents the force applied        by the trailer to the tractor. In case of deceleration the        coupling force is of negative sign.        The mass m_(v) of the vehicle is determined according the prior        art and is not described in detail. The mass m_(v) may be        determined by considering the empty weight of the tractor plus        additional ballast attached thereto. These values may be stored        in the ECU. Alternatively, mass values could be taken from        vehicle acceleration or wheel load detection. A method is        described in applicant's published patent application EP2766239.

The same applies to the determination of the vehicle acceleration a,inclination α and speed v of the vehicle which is described andpractised in the art. Both values may be determined by gyroscope 60which may be part of a GPS navigation system.

The force must be inserted with negative or positive signs according theeffective direction shown in FIG. 6 a.

Similar forces would occur resulting from mass of the trailer andresistances applied on the trailer itself. But the method only considersthe resulting forces applied by the trailer to the tractor, which thecoupling Force F_(C). Only consider parameters applied to the tractorhas the major advantages, that the trailers must not be equipped withsensors or considered in detail. As mentioned above, the variety ofdifferent trailers/implements and their basic technical configurationmay impede detailed considerations of the trailer.

As mainly Coupling Force F_(C) is the relevant parameter to control thetrailer brake system, the equation E1 is changed:

F_(C)=F_(TRC)−(F_(IN)+F_(H)+F_(AR)+F_(R,RA)+F_(R,FA))  (E4)

The forces in brackets represent the Tractive Force of the towingvehicle F_(TRV).

F_(TRV)=F_(IN)+F_(H)+F_(AR)+F_(R,RA)+F_(R,FA)  (E5)

While the Inertia Force F_(IN) and downhill-slope Force F_(H) can beeasily determined during operation using the parameters alreadyavailable on the tractor, the air resistance force F_(AR) and RollResistance Force F_(R,RA), F_(R,FA) is summarised to an OverallResistance Force F_(R).

F_(TRV)=F_(IN)+F_(H)+F_(R)  (E6)

The Overall Resistance Force F_(R) is taken from the graph shown in FIG.6 b in which the vertical axis shows the Overall Resistance Force F_(R)and the horizontal axis shows the vehicle speed v. The graph isdetermined by coast down tests during development and is then stored foreach vehicle series in the ECU. The shown graph is determined for avehicle on asphalt (or road operation). Alternatively, further graphsmay be determined for grassland, farmland or gravel tracks which couldthen be considered when the vehicle is provided with means to detect onwhich terrain the vehicle drives. This may be determined by GPSnavigation system which delivers the geographic information, eg. if thevehicles is driving on a public road (on asphalt), on a gravel track oroffside any road, which may be grassland or farmland.

E.g. in the shown graph the Overall Resistance Force F_(R) at say 25 kphis considered to be 2575 N

So by using equations E1 and E2 and the graph shown in FIG. 6 b theTractive Force of the towing vehicle FTRV can be adequately determinedwith equation E6.

To receive the Coupling Force F_(C), the remaining equation is:

F_(C)=F_(TRC)−F_(TRV)  (E7)

The Tractive Force of the vehicle combination FTRC is determined asknown in prior art by measuring the fluid pressure in a ContinuouslyVariable Transmission (CVT) of the hydrostatic-mechanical split typewhich includes a hydraulic drive circuit in which a hydraulic pumpsupplies pressurized fluid to a hydraulic motor. Details are explainedin applicant's published patent application WO2013/053645 and are noexplained in detail. Alternatively, any other means to determine theTractive Force of the vehicle combination FTRC such as using the torquesupplied by the engine to receive the tractive force as described inU.S. Pat. No. 4 548 079 may be taken instead. (See GB11/44)

The Coupling force can then be received with equation E7.

Using afore mentioned equations and forces the method in FIG. 4 isproceeded. After starting with step 301, a first branch B305 determinesthe Tractive Force of the vehicle combination F_(TRC) in step S335 asexplained above.

A second branch B310 determines the mass m_(v), acceleration a and theinclination α in step S320 as explained above to further calculateInertia Force F_(IN) in step S325 and downhill-slope Force F_(H) in step326.

In a third branch B315, step S330 determines speed v of as explainedabove to further determine Overall Resistance Force F_(R) in step S331with reference to FIG. 6 b.

Second branch B310 and third branch B315 then proceeds into step S340 tocalculate Tractive Force of the towing vehicle FTRV as defined withequation E6.

Finally, the values received in step S335 and S340 are then used tocalculate the actual Coupling Force F_(C. actual) according equation E7.

Alternatively the steps shown in FIG. 4 may be proceeded in one by oneor in any reasonable order.

With reference to FIG. 2 , sub process S300 is permanently proceeded todeliver the actual Coupling Force F_(C,actual) for further steps.

The method M100 in FIG. 2 further continues with permanently monitoringthe status parameter SPCA in step S110 which indicates that the driverstill demands vehicle deceleration via speed foot paddle 71 or drivelever 72. If the activation is interrupted and status parameter SPCA ischanged to zero, the loop L211 resets all parameters in step S115 andreturns to START.

The method M100 in FIG. 2 further continues with step S120 which issetting a first interval counter c, also referred to as the brakeinterval counter) to zero. Then in step S121 a first timer value to isalso set to zero (seconds) and a timer is started. Both parameters areprovided to fulfil the requirements for electronic trailer brake systemsaccording EU-Regulation 2015/68 (dated 15.10.2014), Appendix I, Number2.2.1.19.1 (also referred to as “EU Mother regulation RVBR”) whichlimits the duration of electronically activated trailer braking (withoutthe driver operating the service brake) to a maximum duration of 5 s.After this the trailer brake must be released.

The first time value to is used to monitor the time limit while thebrake interval counter c is used to determine the number of the brakeintervals. A brake interval is thereby characterised by a time period inwhich the electronic trailer brake control is activated/enabled and maybe followed by an optional pause time, in which the trailer brake is notactivated. The next brake interval starts when the trailer brake isactivated again after being in pause. The brake interval is therebyinterrupted if activation requirements as described in step 200 are notmeet and status parameter SPCA returns to zero. This results in thereset of all parameters in step 115 and thereby also the first intervalcounter c and first timer value t₀, discussed in detail herein.

Step S125 checks if the method is currently proceeding in the firstbrake interval (meaning that the time limit has not been exceeded) or ina subsequent brake interval.

If YES step S131 sets the pilot pressure p_(P)=P_(P,0) which solelydepends on the driver deceleration demand DD as determined in step S200.Generally, pilot pressure p_(P) increase with higher decelerationdemand:

If the deceleration results from the operator using the speed footpaddle 71 (resulting in the status parameter SP_(DL)=0), the pilotpressure P_(P,0) is set to 70 kPA.

If the deceleration results from the operator using the drive lever 72(resulting in the status parameter SP_(DL)=1), the pressure leveldepends on setting of the acceleration rate input 73 which is providedby status parameter SP_(AS):

-   -   For SP_(AS)=1 (acceleration rate input 73 set to level I        representing slowest deceleration), the pilot pressure P_(P,0)        is set to 50 kPA.    -   For SP_(AS)=2 (acceleration rate input 73 set to level II), the        pilot pressure P_(P,0) is set to 70 kPA.    -   For SP_(AS)=3 (acceleration rate input 73 set to level III), the        pilot pressure P_(P,0) is set to 100 kPA.    -   For SP_(AS)=4 (acceleration rate input 73 set to level IV), the        pilot pressure P_(P,0) is set to 150 kPA.

The same values are taken if the deceleration results from the cruisecontrol (Receiving YES in step S240) resulting in the status parameterSP_(CC)=1 in step S242 or if the deceleration results from the reversingmode being activated (Receiving YES in step S250) resulting in thestatus parameter SP_(REV)=1 in step S252.

If the deceleration results from the engine speed decrease with stepS260 resulting in YES (and the status parameter SP_(ENG) set to 1), thepilot pressure P_(P,0) is set to 80 kPA

In the embodiment, the set values for pilot pressure P_(P,0) dependingon status parameter SP_(AS) are shared over different decelerationconditions (with one of status parameters SP_(DL), SP_(CA), SP_(CC),SP_(REV), SP_(ENG) set to 1) but may alternatively be defineddifferently for each deceleration conditions.

The values are kept in the ECU and taken considered further in step S140explained herein.

If step S125 shows that the method is currently proceeding in asubsequent brake interval, step S132 sets the pilot pressurep_(P)=p_(P,c) which is the trailer pressure signal TBS generated at stepS150. This results in the advantage that after the end of a brakeinterval, the pilot pressure p_(P) always receives the value which waslast generated in the previous brake interval. This avoids trailer brakesignal peaks between brake intervals which would decrease drivingcomfort.

In step S135, a trailer brake signal TBS is generated, also referred to“First-in-Shot”. This step serves to provide a pressure peak which isused to fill the lines on the trailer. As the trailers in agriculturalbusiness vary in size and therefore also the lines of the trailer brakesystems may vary, this step is provided to keep bias the system and makeit more responsive. The height of the Trailer brake signal TBS, or thetrailer brake actuation pressure must be chosen high enough to fill thelines but low enough to avoid an excessive brake reaction which wouldresult in jerking and negative impact on driving comfort. Therefore the“First-in-Shot” is time controlled and depends on the driverdeceleration demand DD as determined in step S200.

If the deceleration results from the operator using the speed footpaddle 71 (resulting in the status parameter SP_(DL)=0), thefirst-in-shot-pressure P_(FIS) is to 300 kPA and the duration is set to0.03 s

If the deceleration results from the operator using the drive lever 72(resulting in the status parameter SP_(DL)=1), the pressure level andduration depends on setting of the acceleration rate input 73 which isprovided by status parameter SP_(AS):

-   -   For SP_(AS)=1 (acceleration rate input 73 set to level I        representing slowest deceleration), the first-in-shot-pressure        P_(HS) is to 300 kPA and the duration is set to 0.02 s.    -   For SP_(AS)=2 (acceleration rate input 73 set to level II), the        first-in-shot-pressure PFIs is to 300 kPA (alt. 320 kPA) and the        duration is set to 0.03 s.    -   For SP_(AS)=3 (acceleration rate input 73 set to level III), the        first-in-shot-pressure PFIs is to 300 kPA (alt. 340 kPA) and the        duration is set to 0.04 s.    -   For SP_(AS)=4 (acceleration rate input 73 set to level IV), the        first-in-shot-pressure PFIs is to 300 kPA (alt. 360 kPA) and the        duration is set to 0.05 s.

The same values are taken if the deceleration results from the cruisecontrol (Receiving YES in step S240) resulting in the status parameterSP_(CC)=1 in step S242 or if the deceleration results from the reversingmode being activated (Receiving YES in step S250) resulting in thestatus parameter SP_(REV)=1 in step S252.

If the deceleration results from the engine speed decrease with stepS260 resulting in YES (and the status parameter SP_(ENG) set to 1), thepilot pressure P_(P,0) is set to 80 kPA

In the embodiment, the set values for first-in-shot-pressure P_(FIS) isto 300 kPA and the duration depending on status parameter SP_(AS) areshared over different deceleration conditions (with one of statusparameters SP_(DL), SP_(CA), SP_(CC), SP_(REV), SP_(ENG) set to 1) butmay alternatively be defined differently for each decelerationconditions.

In addition, two correction factors f₁, f₂ are multiplied with thefirst-in-shot-pressure P_(FIS) to determine the trailer brake signalp_(TBS):

P_(TBS)=f₁×f₂×P_(FIS)  (E8)

The Correction factor f₁ is in a range between >0 . . . 1 and considersthe fact that with increasing vehicle speed, high First-in-Shot pressurepeaks result in that the trailer tends to jerk which negatively impactsthe driving comfort. On the other hand, when the vehicle combination 1drives downhill, the trailer brake system reaction should be as fast aspossible. The equation for correction factor f₁ is:

$\begin{matrix}{f_{1} = {\frac{v}{v_{Limit}} + \frac{\alpha}{\alpha_{Limit}} - \frac{\alpha*v}{\alpha_{Limit}*v_{Limit}}}} & ( {{E8}\text{.1}} )\end{matrix}$

Whereby

-   -   v_(Limit) is the vehicle speed, below which the First-in-Shot        pressure shall be reduced. This value is set to 25 kph    -   α _(Limit) is the inclination, below which the First-in-Shot        pressure shall be at maximum level independent of the vehicle        speed. This value is set to −5°

The Correction factor f₂ is also in a range between >0 . . . 1 andconsiders the fact pressure level of the “First-in-Shot” is reducedduring the process to avoid overshoots in the trailer brake actuationpressure reducing driving comfort. The equation for correction factor f₂is:

For first brake interval (C=0):

$\begin{matrix}{f_{2} = \frac{p_{P,0}}{p_{Limit}}} & ( {{E8}\text{.2}} )\end{matrix}$

For any subsequent brake interval (C>0):

$\begin{matrix}{f_{2} = \frac{p_{P,c}}{p_{Limit}}} & ( {{E8}\text{.3}} )\end{matrix}$

Whereby

-   -   P_(P,0) is the pilot pressure determined in step S131 taken from        a predetermined parameter set.    -   P_(P,c) is the pilot pressure determined in step S132 taken from        a previous brake interval    -   P_(Limit) is a pressure limit below which the First-in-Shot” is        increasingly reduced. May be 100 kPA

After step the time controlled generation of the trailer brake signalTBS in step S135, step S140 is straight away generating a trailer brakesignal TBS based on the pressure determination as described in Steps131, 132. The trailer brake signal TBS generated in step S135 ismaintained constant until the ECU is generating a further pressuresignal TBS as explained herein.

Applying a pilot pressure depending on the deceleration conditionindicated by an HMI input offers the main advantage that trailer brakeactuation is initially started without determining the physical valuesfor deceleration or coupling force at first so that the trailer brakeactivation is more proactive and faster. Even with step S206 aconsidering a coupling force, the pilot pressure does not depend in sizeat an initial step.

In step S145 the process is waiting for 0.75 s to enable the ECU todetermine the actual coupling force F_(C, actual) as described with stepS300. The waiting period is necessary to consider the effects of thetrailer brake signals TBS generated with steps S135. S140 and theresulting changes in the actual coupling force F_(C, actual). Otherwise,the ongoing process would be based on a coupling force F_(C, actual)which is still changes under the influence of steps S135, S140.

Especially step S140 serve to provide a fast reaction on thedeceleration in form of trailer brake signal TBS based on predeterminedpressure values while in the ongoing process, a 3-point controlalgorithm is applied to determine trailer brake signal TBS. This makesthe system responsive in the first.

The control algorithm is executed with step S400 as explained in detailin FIG. 5 .

Step S400 and the subsequent steps S401 to S490 mainly contains thesteps to control the trailer brake signal TBS by means of a 3-pointcontroller. Generally a 3-point controller represents a discontinuouscontroller type and takes three values, which are 1, 0 and −1. Regardingthe generation of trailer brake signal TBS, trailer brake signal TBS,respective the pressure value is increased, kept constant or decreased.Compared to continuous controller types, such as P, I, or D-Controllersor combinations of them, the 3-point controller tends less toovershooting and can be handled easier in terms of setting parameters toinfluence the controller dynamics. Especially these values may be easieradapted to operating conditions, which may be done by the driver ortrained service personal.

After the start with step S401, step S405 is setting a status parameter,the In-Shot parameter SP_(IS). An In-Shot is a time controlled pressurepeak similar to the First-in-Shot explained with step S135 but isapplied in combination with the 3-point controller. If the In-Shotparameter SP_(IS)=0, no In-shot is provided, if the In-Shot parameterSP_(IS)=1 an In-shot is provided. The in-Shot serves to increaseresponsiveness by supporting the pressure build up in the trailer brakesystem 40. But as pressure peaks may result in jerking of the trailer,the In-Shots may be deactivated if the Coupling force (which ispermanently determined shows) a rapid decrease. As a rapid decrease(determined in Step S300) indicates a fast reaction to trailer brakesignal TBS further In-shots may be omitted. The in-shot is explained inmore detail herein.

In parallel (or subsequently) with steps S405, step S406 is proceeded inwhich the ECU takes the predetermined values defining a coupling forcerange defined by lower coupling force F_(C, L) and a upper couplingforce F_(C,L) which is need to realize a 3-point controller and which isexplained herein.

Next a second interval counter i, also referred to as the controllerinterval counter, is set to zero in step S407.

The controller interval counter i is used to determine the number of thecontrol interval in step S410. In the first interval with counter i=0the method proceeds with step S415 in which the controller pressurep_(PC,0) is set to the value p_(P) which was determined in step S140.

For the next interval (i>0) and with step S416, the controller pressurep_(PC,0) is taken from the subsequent controller interval as stored instep S465 and depicted with p_(PC,i). This results in the advantage thatafter the controller pressure p_(PC,0) always receives the value whichwas last generated in the previous controller interval. This avoidstrailer brake signal peaks between brake intervals which would decreasedriving comfort.

With step S420, the 3-point controller is adjusting the pressure valuesbased on the initial settings of controller pressure p_(PC,0) in stepS415, S416.

Coming back to step S406, the coupling force band defined by lowercoupling force F_(C,L) and upper coupling force F_(C,L) is now explainedin detail. Both values have a negative sign (as they are counteractingthe vehicle) and are needed to operate the 3-point controller.

The lower coupling force F_(C,L) represents a value which shall not beundercut as this may cause the vehicle 10 to become unstable due to theforce applied and the resulting yaw moment about the vertical vehicleaxis. This value is stored in the ECU and may vary for different vehicleconfigurations. E.g. a lightweight vehicle cannot bear the sameforce/yaw moment compared a vehicle 10 with higher weight. The sameapplies depending on wheel base or wheel width which also influence thevehicle stability.

The upper coupling force F_(C,L) represents a value which shall not beexceed as the brake actuation shall be stopped before the coupling forcegets zero. Driver's demand that the trailer is allowed to coast e.g.when the vehicle combination 1 approaches a road crossing. This meansthat a small coupling force is acceptable.

With steps S420, S435 and S437 the 3-point controller checks the valueof the actual coupling force F_(C, actual) relative to the couplingforce band defined by lower coupling force F_(C,L) and upper couplingforce F_(C,L).

If the actual coupling force F_(C, actual) is within the coupling forceband, step S430 is setting the controller pressure p_(PC,i)=p_(PC,0)which means that the pressure value determined in step S415 or S416 istaken without pressure adaption.

If the actual coupling force F_(C,actual) undercuts the lower couplingforce F_(C,L) as checked in step S435, branch B436 is proceeded and stepS438 is setting a controller pressure increase with ΔP_(PC)=ΔP_(PC,set).The value for ΔP_(PC,set) is stored in the ECU and is 15 kPA. Thismeans, that the pressure will be increased to increase brake force onthe trailer.

If step 435 is not met, the actual coupling force F_(C,actual) exceedsthe upper coupling force F_(C,U), branch B437 and step S439 is setting acontroller pressure increase with ΔP_(PC)=−ΔP_(PC,set). This means, thatthe pressure will be decreased to reduce brake force on the trailer.

The method then proceeds in two parallel branches into the stepsencircled with a dotted line 440 which serve to apply the In-shot not.

Following the branch B436, if the In-Shot parameter SP_(IS) was set to 1in step S405 (indicating In-shot activation), step S441 results in thatstep S445 is proceeded. Otherwise the method proceeds to Step 451without applying in-shot. In step S445 the In-shot parameters are set todefine a time-controlled pressure increase with ΔP_(IS)=ΔP_(IC,set) fora duration of t_(IS)=t_(IS1). The value ΔP_(IC,set) and the time t_(IS1)is stored in the CU and is 100 kpa and 0.05 s.

Following the branch B437, if the In-Shot parameter SP_(IS) was set to 1in step S405 (indicating In-shot activation), step S442 results in thatstep S446 is proceeded. Otherwise the method proceeds to Step 451without applying in-shot. In step S446 the In-shot parameters are set todefine a time-controlled in-shot pressure increase withΔP_(IS)=−ΔP_(IC,set) for a duration of t_(IS)=t_(IS2) (which is decreasedue to the negative sign). The value ΔP_(IC,set) and the time t_(IS2) isstored in the CU and is 100 kpa and 0.1 s. The duration in this step isgreater as with step S445 due to the fact that the reaction time of thetrailer brake system is higher when the pressure is decreased. This isbalanced by a longer in-Shot duration.

Both steps S445 and S446 are continued in step S450 in which pressurevalues are set:

As the in-Shot was activated, the In-shot pressure P_(IS) is calculatedby the equation

p _(IS) =p _(PC,0) +Δp _(PC) +Δp _(IS)  (E9.1)

This means that the pressure for the In-shot is received by the sum ofthe controller pressure p_(PC,0) (as set in step S415 or step S416), thecontroller pressure increase ΔP_(PC) (as set in step S438 or step S439)and the in-shot pressure increase with ΔP_(IS) (as set in step S445 orstep S446).

In addition the controller pressure p_(PC,i) is calculated by theequation

P _(PC,i) =P _(PC,0) +Δp _(PC)  (E9.2)

This means that the pressure for the controller pressure is received bythe sum of the controller pressure P_(PC,0) (as set in step S415 or stepS416), the controller pressure increase ΔP_(PC) (as set in step S438 orstep S439) but without the in-shot pressure increase with ΔP_(IS).

In step S455 the ECU generates a trailer brake signal TBS with thetrailer brake signal p_(TBS)=p_(IS) for a duration t_(IS). This stepoverwrites the trailer brake signal TBS generated in step S140 (in FIG.2 ).

If the in-Shot was not activated in steps S441 or S442 the controllerpressure p_(PC,i) is calculated in step S451 by the equation

P _(PC,i) =P _(PC,0) +Δp _(PC)  (E9.3)

After one of step S430 or step S451 or step S455, the method proceedswith step S460 which generates a trailer brake signal p_(TBS)=P_(PC,i)determined in step S430, step S450 or step S451. This brake signal isnot time-controlled and thereby upheld until the next controllerinterval.

The last value of the trailer brake signal TBS is then saved in the ECUwith step S465 for consideration in the next controller interval in stepS416.

Alternatively step S430 may result in that the method is proceeds withstep S465 as there is no pressure increase and the trailer brakepressure generated in step S140 (see FIG. 2 ) is still upheld.

In step S475 the controller interval counter i is increased by 1 forcharacterising an subsequent interval as requested for step S410.

In step S480 the timer value for t₀ is controlled, if the timer value tois below 4 s, the method proceeds with loop L481 which includes stepS485 so that the process is waiting for t₃=0.5 s to enable the ECU todetermine the actual coupling force F_(C, actual) as described with stepS300 and return.

In step S145 the process is waiting for 0.75 s to enable the ECU todetermine the actual coupling force F_(C, actual) as described with stepS300 and then return prior to step 410.

If in step S480, the timer value to exceeds 4 s, step S490 aborts thesub process S400 and returns to main method M100 depicted in FIG. 2 .

To summarise, sub process S400 is continuously adapting the trailerbrake signal TBS by applying the 3-point controller and an optionalIn-shot until the time of 4 s is reached. In the meantime, the processpasses several controller interval, whereby subsequent interval arebased on the trailer brake signal TBS generated in the previousinterval.

Coming now back to FIG. 2 , step S150 saves the last value of thetrailer brake signal in the ECU for consideration in the next brakeinterval in step S132.

Afterwards in step S475 the brake interval counter c is increased by 1for characterising an subsequent interval as requested for step S125.

As already mentioned, the timer value T₀ is provided to ensure that thebrake actuation is not active for more than 5 s. To avoid that thetrailer brake signal TBS (and the brake actuation) abruptly falls tozero, the sub process S400 is aborted after 4 s. The remaining time of 1s is used to ramp down the trailer brake signal TBS to zero before the 5are passed.

Depending on the last trailer brake signal TBS and the cycle time of theECU (which is the time required for the execution of one simpleprocessor operation in the ECU) step S156 calculates a ramp pressuredecrease Δ_(pR) according the equation:

$\begin{matrix}{{\Delta p_{R}} = \frac{t_{c} \times \text{?}}{t_{R}}} & ({E10})\end{matrix}$ ?indicates text missing or illegible when filed

Whereby

-   -   t_(C) is the cycle time of the processes in the ECU, which is 50        ms    -   t_(R) is the ramp time, which is 1 s    -   P_(TBV) is last trailer brake signal TBS

For a last trailer brake signal TBS of 100 kPa equation E10 woulddetermine a ramp pressure decrease Δp_(R) of 4 kPa.

So as long as step S160 does not show that the trailer brake signal TBSis zero, the loop L161 and step S162 is repeatedly proceeded to generatea trailer brake signal TBS which is reduced with Δp_(R). The loop L161is repeated and returns prior to step S160 until the trailer brakesignal TBS is zero.

As long as the activation signal is present in step S165 with SP_(CA)=1the process proceeds with loop L166 in which step S170 contains awaiting period of t₂=1 s and returns prior to step S121 to proceed withthe next brake interval.

If step S165 determines that the activation signal is not present, stepS175 checks if a shut-down condition is met so that the method is endedwith step S180. We have chosen Ignition OFF in step S175.

FIG. 7 briefly depicts the results of the method according theinvention.

The horizontal axis depicts the time in which the method proceeds.

The vertical axis is shows two portions:

-   -   The upper portion depicts the trailer brake signal TBS with        pressure p_(TBS)    -   The lower portion depicts the measured coupling force        F_(C,actual) as determined with step S300 including the coupling        force band defined by F_(C,U) and F_(C,L) whereby F_(C,U)=−2000        Newton and F_(C,L)=−4000 Newton. The graph B of the measured        coupling force F_(C,actual) is smoothened as with the cycle time        of 50 ms the curve would show permanent oscillations

As best seen with graph A the timer value for t₀ is set to zero at stepS121. As this is the first brake interval with C=0, step S131 determinesthe Pressure value P_(FIS) of the First-In-Shot which is then generatedat step S135. During the waiting period in step S145, the Pilot pressureP_(P) is kept. Then the process proceeds to step S400.

Based on the actual pressure, the In-Shot with p_(IS) is applied withstep S455 based on the determination in steps S438, S445, S450. Then, instep S460, the controller pressure P_(PC) is generated based on thedetermination in step S438. The steps S438, S445, S450 deliver anpositive pressure increase as the coupling force F_(C,actual) is belowF_(C,L). This is repeated until the coupling force F_(C,actual) is abovethe F_(C,L). Then a negative pressure increase is determined in stepsS439, S446, S450 for generating the in-shot p_(IS) in S455 and thecontroller pressure P_(PC) in step 460.

This is provided until in step S480, timer t₀ reaches 4 s and the3-pont-controller is aborted. Next, the trailer brake signal TBS andpressure p_(TBS) is ramped down in steps L161/s162. After 5 s (overall,or 1 s of down ramping) the pressure p_(TBS) is to zero. A waitingperiod of 1 s is then applied with step S170.

If the activation signal is kept alive, the process starts again withthe next brake interval (c=1), but then starts with the pressure valueform previous interval P_(PC,1) through step S132 and appliesFirst-in-Shot, In-shot and Pressure control as described before.

At the time indicated with dotted line X the coupling force F_(C,actual)is in the coupling force band so that the trailer brake signal TBS andpressure p_(TBS) remains unchanged until the 4 s are reached again andramping down starts.

A further embodiment of the invention relates to the generation ofwarning messages provided to the driver which may include furtherembodiments of the invention provided to detect if the trailer isattached, and moreover, for trailers provided with a brake system,determining the temperature of the trailer brake system.

With reference to FIG. 2 the process branches off to proceed sub processS500 in parallel, e.g. to sub process S300.

With reference to FIG. 8 , sub process S500 is provided to generatewarning messages on HMI terminal 75. Alternatively, the information maybe indicated to the driver via an audio means or any other suitablemeans.

Sub process S500 starts with step S501 and proceeds further with step505 to check if the electronic trailer brake function is activated (withETCV=1). Preferably, the electronic trailer brake function is alwaysactivated during operation, e.g. when ignition is ON and/or theelectronic vehicle control unit ECU is energized.

In Step S508 the process initially sets the parameter SP_(DT1) to 0 as adefault condition. The parameter SP_(DTI) is a status parameterindicating that the detection of the trailer in sub process S600 wasproceeded correctly as explained below. As this has not been provided atthat stage, parameter SP_(DT1) is set to 0 before sub process S600starts. As explained below the provision of parameter SP_(DT1) alsoenables the method to be processed without trailer detection.

The next step starts sub process S600 to provide the trailer detectionand next sub process S700 to determine the trailer brake temperature. Asindicated above, sub process S600 is an optional step.

With reference to FIG. 9 , sub process S600 is now explained in detail.Similar to step S508, step S615 sets the parameter SP_(DT1) to 0 toprovide a default condition. The process then branches to step S605 inwhich the activation of the electronic trailer brake function ischecked, if not active (ETCV=0) the process returns prior to step S615,If the electronic trailer brake function is active (ETCV=1) the stepsS610 to S614 serve to check further parameters which are explainedbelow, whereby the order may be changed:

-   -   In step S610 the process checks if the vehicle is driving on a        slope. If the current inclination α is greater than inclination        α_(TD,min) (which may be about 3°) the process proceeds with        next parameter, if the current inclination α is below, process        returns to returns prior to step S615.    -   In step S611 the process checks if the trailer brake pressure        p_(TBS) stored in step S150 (shown in FIG. 2 ) is greater than        p_(TBSTD,min) (which may be about 80 kPA). If YES, the process        proceeds with next parameter, if the current trailer brake        pressure p_(TBS) is below p_(TBSTD,min), the process returns to        returns to step S615. This step serves to check if the last        stored and applied trailer brake signal was above a level which        results in that the trailer brake supplies a brake effort. Tests        have shown, that below P_(TBSTD,min) the signal does not result        in effective braking of the trailer but only results in that        that the brake lines are filled or the brake actuators move to        slightly contact the brake discs.    -   In step S612 the process checks if the service brake of the        tractor is not activated (SP_(SB)=0). If YES, the process        proceeds with next parameter, if NO (SP_(SB)=1) the process        returns to returns to step S615. Any activation of the service        brake would overwrite electronic trailer braking provisions        mentioned above.    -   In step S613 the process checks if the park brake of the tractor        is not activated (SP_(PB)=0). If YES, the process proceeds with        next parameter, if NO (SP_(PB)=1) the process returns to returns        to step S615. Any activation of the park brake would overwrite        electronic trailer braking provisions mentioned above.    -   In step S614 the process checks if the current inclination α        remains within an inclination band by lower value α_(TD,L1) say        3°, and upper value α_(TD,L2) say 20°. If YES, the process        proceeds with step S620, if NO the process returns to returns to        step S615. In other words, the vehicle must remain on the slope        during trailer detection.

It is envisaged that the parameters α_(TD,min), p_(TBSTD,min),α_(TD,L1), α_(TD,L2) used for these comparisons and also statusparameters SP_(SB) and SP_(PB) may be stored in the ECU and may vary fordifferent vehicle configurations. Some of the conditions may be usedoptionally.

If conditions are not met, process returns to returns to step S615 sothat the parameter SP_(DT1) remains 0 for usage in other processes,especially S500. This means that the trailer detection failed.

If all conditions are met, step S620 sets the parameter SP_(DT2)=0 toprovide the default condition. The parameter SP_(DT2) is a statusparameter indicating that a trailer was detected (SP_(DT2)=1) or if thetractor is operated without trailer (SP_(DT2)=0) and is explained belowin detail.

In step S625 the process includes a timer loop which waits until thefirst timer value to is also set to zero (seconds) in STEP S121 to startthe timer for the brake interval. Briefly described, step S625 enablesthat the subsequent process is processed in parallel to the stepsfollowing step S121 in main process M100 to define the brake interval asdescribed in FIG. 2 . Alternatively, the brake interval counter c asdescribed in FIG. 2 may be used to determine the duration of the brakeinterval.

In step S630, the process determines an average coupling force valueF_(DT) within a predetermined number of cyles n_(TD) based on thepermanent determination of the coupling force F_(C,actual) as describedwith step S300 in FIG. 3 . This parameter is used to detect the presenceof the trailer as described below.

In step S635, the process includes a further timer loop which waitsuntil the first timer value t₀ reaches 4 seconds. As described in themain process M100 (FIGS. 2 ) and S400, if the timer value is 4 seconds,the trailer brake pressure signal F_(TBS) is ramped down in steps S160,S162.

Step S640 saves a first averaged coupling force value F_(TD1) determinedbased on step S630. Further details are described below.

In Step S645 the process waits until trailer brake pressure signalF_(TBS) is ramped down to F_(TBS)=0 with steps S160/S162.

With the trailer brake pressure signal F_(TBS)=0, step S650 saves asecond averaged coupling force value F_(TD2) determined based on stepS630. Further details are described below.

In step S655 the process waits for an time offset Δt_(TD)=0.5 seconds.At this time, the trailer brake pressure signal F_(TBS) is increasedagain with the next brake interval (indicated with c).

Step S660 saves a third averaged coupling force value F_(TD3) determinedbased on step S630.

The values of the first, second and third average coupling force valuesF_(TD1), F_(TD2), F_(TD2), in steps S640, S650 and S660 now enable theelectronic vehicle control unit ECU to determine parameters of thetrailer detection according a further aspect of the invention in stepS665 and S670 which is now explained in more detail with reference toFIG. 12 .

FIG. 12 briefly depicts the the time in which the method proceeds in thehorizontal axis.

The vertical axis is shows two portions:

-   -   The upper portion depicts the trailer brake signal TBS with        pressure P_(TBS)    -   The lower portion depicts the averaged coupling force F_(TD) as        determined with step S630. The graph B of the averaged coupling        force F_(TD)

In step S665 the process checks the subtraction F_(TD2)-F_(TD1) isgreater than a first difference value Δ F_(TDL) stored in the ECU, whichis assigned to a reduction of the trailer brake pressure. With referenceto FIG. 12 , this is done to check if the ramp down of the pressureduring step S160/162 (described with FIG. 2 ) results in a significantchange in the coupling force when considering that the force applied bythe trailer to the tractor is of negative sign. If no trailer with atrailer brake system is attached, the release of the trailer brake wouldnot impact the coupling force. If a trailer with a trailer brake systemis attached (and the conditions as described in steps S610 to S614 aremet) the coupling force increases in negative sign direction as thetrailer pushes the tractor without trailer braking. In the shownembodiment, F_(TD1) is about −3000 N and F_(TD2) is about −3500 N. Asthe predetermined value for Δ F_(TDL)=−300 N, the subtraction F_(TD2)−F_(TD1) would result in −500 N being greater than the first differencevalue Δ F_(TDL) in negative sign direction. With the condition of stepS665 being met, process moves to next step S670. If not met, processmoves to prior to step S680 explained below.

In step S670 the process checks the subtraction F_(TD3)-F_(TD2) isgreater than a second difference value Δ F_(TDR) stored in the ECU,which is assigned to an increase of the trailer brake pressure. Withreference to FIG. 12 , this is done to check if raising the trailerbrake pressure in the next brake interval starting with steps S460 in(described with FIG. 5, 11A, 11B) results in a significant change in thecoupling force when considering that the force applied by the trailer tothe tractor is of negative sign. If no trailer with a trailer brakesystem is attached, the increase of the trailer brake pressure would notimpact the coupling force. If a trailer with a trailer brake system isattached (and the conditions as described in steps S610 to S614 are met)the coupling force would decrease in negative sign direction as thetrailer tractor combination is stretched reducing pushing effect. In theshown embodiment, F_(TD3) is about −3200 N and F_(TD2) is about −3500 N.As the predetermined value for Δ F_(TDR)=200 N, the subtractionF_(TD3)-F_(TD2) would result in 300 N being greater than the seconddifference value Δ F_(TDR). With the condition of step S665 being met,process moves to next step S670. If not met, process moves to prior tostep S680 explained below.

If the conditions defined in steps S670 and S675 are met, the processapproaches to step S675 in which the parameter SP_(DT2) is set to 1indicating that a trailer was detected.

If the conditions defined in steps S670 and S675 are not met, steps S670and S675 approach to step S680 in which the parameter SP_(DT2) is set to0 indicating that tractor is operated without a trailer.

Compared to the parameter SP_(DT2), the parameter SP_(DT1) just statesif the trailer connection failed or not in that parameter SP_(DT2) isset to 0 or 1. If not parameter SP_(DT1) remains 0.

With loop L685, the process returns prior to step S635 to restart thecoupling force determination to continually determine status parametersSP_(DT1) and SP_(DT2) and forward the results to other sub routines,especially the subroutine S500 in FIG. 8 . Alternatively, the subroutine S600 may end with step S690 so that the status parametersSP_(DT1) and SP_(DT1) are only determined during two brake intervals.Sub process S600 may then be restarted with step S508 in sub routineS500.

Coming back to FIG. 8 , sub process S500 then proceeds with further subroutine S700 which is provided to determine a trailer brake temperature.

With reference to FIG. 10 , sub routine S700 starts with step S701. Instep S705, a temperature correction factor K_(TP) is set to 0 as adefault condition. Further details are explained below.

in step S710, a time value t_(TP) is set to 0. Further details areexplained below.

The steps S715 and S716 are provided to check certain operatingconditions:

-   -   Step S715 ensures that the vehicle is moving on relatively flat        terrain with α_(TPmax)>α>αTP_(min), whereby α_(TPmin)=1° and        α_(TPmax)=5° stored in the ECU as setting.    -   Step S716 ensures that the vehicle speed v_(v) remains constant

If these conditions are met within the duration defined with step S720and the time loop L721, e.g. 2 seconds, the process proceeds with stepS752 explained below.

If these conditions are met within the duration defined with step S720and the time loop L721, the process proceeds with step S730 to determinean average coupling force value F_(TP) within a predetermined number ofcycles n_(TP) based on the permanent determination of the coupling forceF_(C, actual) as described with step S300 in FIG. 3 . As the conditionsdefined in steps S715 and S716 mean that the vehicle combination isoperated in a condition wherein the tractor pulls the trailer (notrailer brake activation) the average coupling force value F_(TP) isdetermined in positive sign, which is important for the next steps,S740, S74, in which the average coupling force value F_(TP) is used toprovide a rough information on the weight of the trailer. As the trailerweight is one important factor impacting the trailer brake temperatureduring brake activation, average coupling force value F_(TP) is taken toestimate trailer weight and set a temperature correction factor K_(TP)accordingly as explained below:

If in step S740, the average coupling force value F_(TP) is below afirst limit value F_(TP,limit1), e.g. 500 Newton, this would indicatethat a light weight trailer is attached so that the temperaturecorrection factor K_(TP) is set to 0.6 in step S750.

If the condition in step S740 is not met, the process continues with tostep S741.

If in step S741, the average coupling force value F_(TP) is within afirst limit value F_(TP,limit1) and a second limit value F_(TP,limit2)e.g. between 500 N and 1500 N, this would indicate that a medium weighttrailer is attached so that the temperature correction factor K_(TP) isset to 0.8 in step S751.

If step S740 or S741 are not met, the average coupling force valueF_(TP) must exceed second limit value F_(TP, limit2) e.g. 1500 N, thiswould indicate that a heavy weight trailer is attached so that thetemperature correction factor K_(TP) is set to 1 in step S752. Thetemperature correction factor K_(TP) is also set to 1 in step S752, ifthe conditions defined in step S715 and S716 are not met within theduration defined with step S720 and the time loop L721.

To summarise, depending on an average coupling force value F_(TP) thesteps starting with S730 provide an estimation of the vehicle weight, ormore precise, assign three trailer weights light weight, medium weight,heavy weight depending on the average coupling force value F_(TP) to settemperature correction factor K_(TP).

This temperature correction factor K_(TP) is used to adapt a trailerbrake temperature TP_(TBS,DEF).

Initially, step S760 determines a trailer brake temperature TP_(TBS,DEF)using a temperature model. The temperature model may use parameters suchas the trailer brake pressure T_(TBS), the trailer brake durationt_(TBS) (how long the trailer brake pressure is kept) and furtherparameters such as the ambient temperature TP_(Ambient). Trailer brakepressure T_(TBS) and the trailer brake duration t_(TBS) may bedetermined during e.g. M100 or sub routine S400. The ambient temperaturemay be already available in the ECU, e.g. for HVAC control.

Thereby it is considered the fact that brakes (or clutches) tend toproduce more heat with higher trailer brake pressure T_(TBS) and longertrailer brake duration t_(TBS). The same applies when the vehicle ortrailer is operated in hot ambient conditions. A major drawback of thismodel is that the trailer weight is not included.

The temperature model is not explained in detail as this is known formmany applications for brakes, but also for clutches in vehicles orstationary applications.

In step S770, the process calculates the trailer brake temperatureTP_(TBS) by multiplication of TP_(TBS,DEF) with temperature correctionfactor K_(TP).

Sub Routine may end with step S790.

To summarise, process S700 estimates the trailer weight based on the(average) coupling force during pull operation and corrects the braketemperature (determined by a known temperature model) so that thesubroutine delivers a lower trailer brake temperature TP_(TBS) for alight weight trailer (as the heat impact is lower when the weight issmaller) and higher trailer brake temperature TP_(TBS) for a medium orheavy weight trailer (as heat impact increases with trailer weight). Asthe trailer brake temperature TP_(TBS) is further used to generatetemperature warning to the driver, the process has the major advantagethat the trailer brake temperature is considering trailer weight.

Coming back to FIG. 8 and sub routine S500, with the parameters of thetrailer detection and the trailer brake temperature determined, Subroutine S500 proceeds to generate warning messages as explained below:

In step S510, the process checks of the trailer detection failed. IfYES, the process commences with step S525. If the trailer detection wasprocessed correctly, step S515 checks if a trailer is attached or thetractor (SP_(TD2)=1) is operated without trailer.

If the condition SP_(TD2)=1 is met, the process commences with step S525to set a warning level parameter WL to 0 as default. Thus default valuerepresents a condition in which the trailer brakes are at a level whichdo not require to impact the method described herein.

In step S530 the process checks if the trailer brake temperatureTP_(TBS) determined in subroutine S700 exceed a first temperature limitT_(TBS,L1). If NO, a loop returns the process prior to step S525. Inother words, the process waits until first temperature limit _(TBS,L1)is exceeded before further processing.

If the condition is met, step S535 sets warning level parameter WL to 1which indicates that a first warning level is reached. As a result stepS536 generates a first temperature message (temperature LEVEL 1) shownthe HMI terminal 75 as depicted in FIG. 13A. The message includes atemperature bar display 800 representing trailer brake temperatureTP_(TBS) in a graphical format. Temperature bar display 800 containsthree coloured partitions:

-   -   A portion 800 a representing a trailer brake temperature        TP_(TBS) below TP_(TBS), L1 (WL=0) depicted in GREEN colour.    -   A portion 800 b representing a trailer brake temperature        TP_(TBS) in a range between TP_(TBS,L1) and TP_(TBS,L2) (WL=1)        depicted in ORANGE colour then.    -   A portion 800 c representing a trailer brake temperature        TP_(TBS) exceeding TP_(TBS, L2) (WL=2) depicted in RED colour.        Portion 800 c is greyed out in step S536.

Furthermore a warning message 801 is generated to prompt the driver thatthe trailer brake temperature is high and recommend to reduce vehiclespeed. In combination with first temperature message, step S537 showsthe status of the electronic trailer braking including a symbol 810 aindicating that the electronic trailer braking remains activated.

If the trailer detection has failed as checked in step S537 (withSP_(TD1)=0) an additional message 820 would be generated in step S539 asdepicted in FIG. 13B to inform the driver that the trailer detectionfailed. Warning message 801 as depicted in FIG. 13 a may be appearalternatingly.

In parallel step S540 sets a pressure limit value P_(TBS,max) to apredetermined value stored in the ECU. This pressure value is used tolimit the trailer brake pressure signal p_(TBS) as explained lateronwith FIG. 11A, 11B.

In next step S550 the process checks if the trailer brake temperatureTP_(TBS) remains in a range between TP_(TBS, L0) and TP_(TBS, L1). Thismeans that warning level parameter WL=1 remains unaltered. If YES, theprocess returns via loop L551 prior to step S535.

Before going further, the previously described process was described forthe parameter SP_(TD2)=1 with a trailer detected. If in step S515 isSP_(TD2)=0 the tractor is operated without trailer and commences withbranch B516 to step S520. Step S520 is provided to check (similar tostep S530) if the trailer brake temperature TP_(TBS) exceed a firsttemperature limit _(TBS,L1). If NO, a loop returns the process prior tostep S525. If the condition is met, the process follows branch B521 tostep 560. In other words, the process skips the temperature warningLEVEL 1 initiated by the warning level parameter WL=1 and insteadinitiate next temperature warning LEVEL 2. This has the majoradvantages, that when the status of the trailer detection indicates thatthe tractor is operated without a trailer, a warning level is generatedonly when the temperature exceeds a higher level so that the driver maycheck if a trailer is attached without being detected. This may beimprove safety but avoid showing to many warnings.

Alternatively, the process may commence after step S520 by followingalternative branch B522 to deactivate electronic trailer braking asexplained with step S570.

In step S560 the process checks if trailer brake temperature TP_(TBS)exceeds TP_(TBS, L2). If NO, the process returns via loop L561 prior tostep S525. If YES, next temperature level is reached and warning levelparameter WL set to 2 in step S565.

As a result step S566 generates a second temperature message(temperature LEVEL 2) shown the HMI terminal 75 as depicted in FIG. 13 c. The message includes a temperature bar display 800 representingtrailer brake temperature TP_(TBS) in a graphical format. Temperaturebar display 800 contains three coloured partitions:

-   -   A portion 800 a representing a trailer brake temperature        TP_(TBS) below TP_(TBS), L1 (WL=0) depicted in GREEN colour.    -   A portion 800 b representing a trailer brake temperature        TP_(TBS) in a range between TP_(TBS,L1) and TP_(TBS,L2) (WL=1)        depicted in ORANGE colour.    -   A portion 800 c representing a trailer brake temperature        TP_(TBS) exceeding TPTBS, L2 (WL=2) depicted in RED colour.

If the trailer detection has failed as checked in step S567 (withSP_(TD1)=0) an additional message 820 would be generated in step S568 asdepicted in FIG. 13D to inform the driver that the trailer detectionfailed.

In step S570 the electronic trailer braking is deactivated by settingthe ETCV=0 so that a message is generated in step S571 shown a symbol810 b indicating that the electronic trailer braking is deactivated.

With the process further approaches along branch L575 step S580 checksif trailer brake temperature TP_(TBS) falls below TP_(TBS, L0).TP_(TBS, L0) is a temperature level which indicates that the brakes havecooled down sufficiently after exceeding the previous temperaturevalues. If NO, the process returns via loop to wait until the conditionis met. If YES, the process approaches to step S585 in which theelectronic trailer braking is activated (again) and the symbol 810 a(similar to FIG. 13A) is shown again. The process then returns prior tostep S600.

Regarding the temperature limits, the values are depicted in FIG. 13Awhereby TP_(TBS, L0)<TP_(TBS, L1)<TP_(TBS, L2).

The above described messages may be confirmed by the driver todisappear. Alternatively, the messages may disappear after a certaintime. More alternatively, the messages may be shown in large scale onthe HMI 75 and reduced to a smaller size after a certain time period.Instead of an optical message, the message may be provided by voice orany other suitable means having the attention of the driver.

To summarise, sub routine S500 is designed to provide a two stagetemperature warning when the trailer detection has worked properly andan attached trailer with a trailer brake system is detected. Inaddition, for the case that the trailer detection failed, the two stagetemperature warning is kept, but the driver is additionally prompted tocheck if a trailer is attached. This may point the attention to thedriver that he has to regularly check trailer brake temperatures ormonitor if brake fading occurs as the described process is not able todependably provide this important information.

When the trailer detection has been processed successfully and thetrailer detection indicates that the tractor is operated withouttrailer, the process skips first warning level. Even if there may be notrailer, the driver is still informed, but only at higher trailer braketemperatures to make sure that if the detection was wrong in any otherway the driver is informed in this case of high brake temperaturelevels. E.g. if a trailer with trailer brake system is attached, but thetrailer brake system is not correctly connected to the tractor so thatthe trailer brake signal p_(TBS) is not correctly forwarded to thetrailer to initiate braking, the driver is pointed to that problem andcan check the connection.

As already indicated in the preceding description the temperaturemonitoring and warning process also influence the trailer brake signalp_(TBS) which is now described with reference to FIGS. 2, 8, 11A, 11B,12A and 12B.

FIG. 11A and 11B is similar to FIG. 5 but split into two portions forclarity reasons. Where the same elements and references are used as inFIG. 5 , these are not described again. The flow chart depicted in FIG.11A and 11 b are provided with triangular transition markers a, b, c, dand e to emphasize how the process of FIG. 11A and FIG. 11B isconnected.

As described in FIG. 8 , the step S535 sets warning level parameter WL=1and step S540 sets a pressure limit value p_(TBS,max) at a firsttemperature LEVEL 1. Furthermore, step S565 sets warning level parameterWL=2 when a second temperature LEVEL 2 is reached. The parameters WL andP_(TBS,max) are used in sub routine S400 depicted in FIG. 11A and 11B tocontrol the trailer brake signal p_(TBS) as described in the following:

In step S805 the subroutine S400 checks if temperature level is at LEVEL2. If YES, the process skips to the end at step S490. This will, withreference to FIG. 2 , result in that step S160 and S162 ramp down thepressure to p_(TBS=)0. In other words, when very high temperatures arereached, the trailer brake is brought into a condition where the brakesare not operated so that they may cool down. This is schematicallydepicted with FIG. 14A wherein the time in which the method proceeds isdepicted in the horizontal axis and the vertical axis shows the trailerbrake signal TBS with pressure p_(TBS). The dotted line graph G1represent the trailer brake signal p_(TBS) for the case that warninglevel parameter WL=0, so no critical temperature indicating temperatureLEVEL 1 or LEVEL 2 is reached. While solid line graph G2 represents thetrailer brake signal TBS when temperature LEVEL 2 (WL=2) is reached.

If the temperature LEVEL 2 (WL=2) is not reached, process commences withstep S420 to start the trailer brake signal generation depending oncoupling force as previously described in FIG. 5 . If condition in stepS420 is met the branch B811 with step S430 remains as described in FIG.5 and is therefore not described further. If NO, branch B812 isproceeded with step S435.

If step S435 is not met, meaning that the actual coupling forceF_(C, actual) exceeds the upper coupling force F_(C,U), branch B437 andstep S439 is proceeded as described in FIG. 5 and not described further.In other words, the controller pressure p_(PC,i) can still be reduced asdescribed in step S439, S442, S446.

If the actual coupling force F_(C,actual) undercuts the lower couplingforce F_(C,L) as checked in step S435, branch B436 is proceeded. As inthe process described in FIG. 5 , this may initially result in anincrease of controller pressure p_(PC,i), but step S820 first checks iftemperature LEVEL 1 (WL=1) is reached. If NO, the process proceeds withbranch B 821 and step S438 to increase the trailer brake pressure signalp_(TBS) as described in FIG. 5 and therefore not described further.

If step S820 determines that temperature LEVEL 1 (WL=1) is reached themethod proceeds with branch B822 to step S830 to set the pressureincrease Δp_(TP) to 0. This results in that the pour is not increasedfurther in step S835.

With reference to FIG. 11B the process then passes further viatransition marker c to step S840 where the method checks if temperatureLEVEL 1 (WL=1) is reached. If temperature LEVEL 1 (WL=1) is not reached,branch B841 is processed to generate a trailer brake signalp_(TBS)=p_(C,i) in step S460. If temperature LEVEL 1 (WL=1) is reached,the process checks in step S850 if the trailer brake pressure signalp_(C,I) is below pressure limit p_(TP, max). If NO, the trailer brakepressure signal p_(C,I) is set to p_(TP, max) in step S860 and thenproceeds back to branch B841 and step 460 to generate a trailer brakesignal P_(TBS)=p_(C,I)=p_(TP, max) If YES the process returns to branchB841 to generate a trailer brake signal p_(TBS)=p_(c,i) in step S460without limitation of the brake pressure. Steps S840, S850 and S860serve to enable the process to keep trailer brake pressure signalp_(C,I) (determined in a previous controller interval i) constant, butif the trailer brake pressure signal p_(C,I) once falls below pressurelimit p_(TP, max) the limit is not exceeded as long as the activation ofthe electronic trailer brake is active with SP_(CA)=1.

The result of the process can be best seen in FIG. 14B wherein the timein which the method proceeds is depicted in the horizontal axis and thevertical axis shows the trailer brake signal TBS with pressure P_(TBS).The dotted line graph G3 represent the trailer brake signal p_(TBS) forthe case that warning level parameter WL=0, so no critical temperatureindicating temperature LEVEL 1 or LEVEL 2 is reached. While solid linegraph G4 represents the trailer brake signal TBS when temperature LEVEL1 (WL=1) is reached. Graph G4 shows that the trailer brake signalp_(C,i) can be kept at a constant level (with steps S430 or S835) whichmay be above pressure limit p_(TP, max) or be reduced with step S446 butif the pressure once drops below pressure limit p_(TP, max), steps850/860 ensures that the controller pressure p_(PC,i) cannot beincreased above the value of the pressure limit p_(TP, max), even if achange in the coupling force may require according step S435. Graph G5depicts that the limitation is kept even when next interval C start aslong as the activation was not aborted. This prohibits increased heatimpact by generating an increased trailer brake pressure whentemperature LEVEL 1 is reached.

The further steps S465 to S490 remain as described in FIG. 5 andtherefore not described further.

To summarize, the method according invention ensures that

-   -   when temperature LEVEL 2 is reached, the controller pressure        p_(PC,i) and thereby the trailer brake signal p_(TBS) is ramped        down immediately. As the trailer brake signal is not abruptly        cut the driver can easier experience the changing situation        assisted by the display warnings.    -   when temperature LEVEL 1 is present, the method enables to keep        trailer brake signal p_(TBS) at the same level or reduce the        trailer brake signal p_(TBS) depending on coupling force. Again        this avoids abruptly cutting trailer brake signal so that the        driver can easier experience the situation assisted by the        display warnings.    -   When temperature LEVEL 1 is present, the method also ensures        that the coupling force does not result in a trailer brake        signal p_(TBS) which exceeds the pressure limit p_(TP, max) when        once below the pressure limit p_(TP, max) This helps to cool the        trailer brakes down to a more acceptable level.    -   When none of the temperature LEVEL 1 or LEVEL 2 condition is        present, the trailer brake signal p_(TBS) can be increased or        decreased depending on coupling force.

1. A control system for controlling operation of a trailer brake systemassociated with an agricultural vehicle, the control system comprising avehicle control unit, and being configured to: determine a couplingforce associated with a coupling point for providing a coupling betweenthe vehicle and a trailer; determine, in dependence on the couplingforce, the presence of a trailer coupled to the vehicle at the couplingpoint; generate and output a control signal for controlling at least onecomponent of the vehicle in dependence on the determination of thepresence of the trailer; and control a user interface of the vehicle toprevent issuance of a warning message associated with the trailer independence on the determination that no trailer is present.
 2. Thecontrol system of claim 1, further configured to determine the couplingforce at a plurality of time points within a brake interval of thetrailer braking system.
 3. The control system of claim 2, furtherconfigured to determine a change in a determined coupling force duringthe brake interval through comparison of the determined coupling forceat at least two of the plurality of time points within the brakeinterval.
 4. The control system of claim 2, wherein the brake intervalis defined by a trailer brake pressure signal provided by the controlsystem for controlling the trailer brake system.
 5. The control systemof claim 4, wherein a first time point of the brake interval correspondsto a time point when the trailer brake pressure signal is controlled toprovide an operating pressure level in at least one fluid line of thetrailer brake system.
 6. The control system of claim 5, wherein a secondtime point of the brake interval corresponds to a time point when thetrailer brake signal is reduced to reduce the pressure level in one ormore fluid lines of the braking system to reduce a braking effectprovided by the trailer brake system.
 7. The control system of claim 6,further configured to determine a difference between the coupling forceat the first and second time points and compare the force differencewith a first difference value to determine the presence of a trailercoupled to the vehicle.
 8. The control system of claim 7, furtherconfigured to determine that a trailer is present in dependence on thedetermined difference between the coupling force at the first and secondtime points being greater than the first difference value, and todetermine that a trailer is not present in dependence on the determineddifference being less than the first difference value.
 9. The controlsystem of claim 6, further configured to determine a coupling forceassociated with an increase in the trailer brake signal during asubsequent brake interval of the trailer braking system.
 10. The controlsystem of claim 9, further configured to determine a difference betweenthe coupling force associated with the subsequent brake interval and thecoupling force determined for the second time point of the brakeinterval, and to compare the difference with a second difference value.11. The control system of claim 10, further configured to determine thata trailer is present in dependence on the determined difference betweenthe coupling force at the second time point and during the subsequentbrake interval being greater than the second difference value, and todetermine that a trailer is not present in dependence on the determineddifference being less than the second difference value.
 12. The controlsystem of claim 1, further configured to determine an inclination of thevehicle to determine if the vehicle is driving on a slope, and todetermine the presence of a trailer in dependence on the vehicleinclination.
 13. The control system of claim 12, further configured tocompare the determined inclination of the vehicle with upper and lowerinclination thresholds, and determine the presence of a trailer independence on the determined inclination being between the upper andlower inclination thresholds.
 14. The control system of claim 1, furtherconfigured to check activation of at least one additional braking systemassociated with the vehicle, and to determine the presence of a trailerin dependence thereon.
 15. (canceled)
 16. The control system of claim 1,further configured to determine the coupling force in dependence on ameasure of an operating parameter of a transmission of the vehicle. 17.The control system of claim 1, further configured to determine thecoupling force in dependence on at least one measurement signal receivedfrom a sensor associated with the coupling point.
 18. A braking systemcomprising the control system of claim
 1. 19. An agricultural vehiclecoupleable to a trailer to form a vehicle-trailer combination, andcomprising the control system of claim
 1. 20. A method of controllingoperation of a trailer brake system associated with an agriculturalvehicle, the method comprising: determining a coupling force associatedwith a coupling point for providing a coupling between the vehicle and atrailer; determining, in dependence on the coupling force, the presenceof a trailer coupled to the vehicle at the coupling point; controllingat least one component of the vehicle in dependence on the determinationof the presence of the trailer; and controlling a user interface of thevehicle to prevent issuance of a warning message associated with thetrailer in dependence on the determination that no trailer is present.21. The method of claim 1, further comprising determining the couplingforce at a plurality of time points within a brake interval of thetrailer braking system.